Device and method for reducing carbon dioxide

ABSTRACT

A device for reducing carbon dioxide includes a vessel for holding an electrolyte solution including carbon dioxide, a working electrode and a counter electrode. The working electrode contains boron particles.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of PCT Application No. PCT/JP2011/001521 filed on Mar. 15, 2011, claiming priority of Japanese Patent Application No. 2010-165649 filed on Jul. 23, 2010, the entire contents of each of which are incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to a device and a method for reducing carbon dioxide.

SUMMARY

One of the purposes of the present disclosure is to provide a novel device and method for reducing carbon dioxide.

One example of the present disclosure is a device for reducing carbon dioxide. The device includes a vessel for holding an electrolyte solution including carbon dioxide, a working electrode and a counter electrode. The working electrode contains boron.

In the above device, the counter electrode may contain one of platinum, gold, silver, copper, nickel and titanium.

In any of the above devices, the working electrode may contain boron particles disposed on a substrate. The substrate may be a carbon paper, a noble metal substrate, a glassy carbon substrate or a conductive silicon substrate.

Any of the above devices may optionally include a solid electrolyte membrane interposed between the working electrode and the counter electrode. Further, any of the above devices may optionally include a reference electrode.

Another example of the present disclosure is a method for reducing carbon dioxide by using any of the above devices for reducing carbon dioxide. The method includes a step (a) of preparing any one of the aforementioned devices. An electrolytic solution is held in the vessel, the boron in the working electrode is in contact with the electrolytic solution, the metal in the counter electrode is in contact with the electrolytic solution, and the electrolytic solution contains the carbon dioxide. The method further includes a step (b) of applying a voltage between the working electrode and the counter electrode, thereby reducing the carbon dioxide contained in the electrolytic solution.

In the above method, in the step (b), the voltage applied between the working electrode and the counter electrode is not less than 2.0 volts. In the step (b), at least one of methane, ethylene, ethan, and formic acid is generated.

The present disclosure can provide a novel device and method for reducing carbon dioxide.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an exemplary device for reducing carbon dioxide according to the embodiment 1.

FIG. 2 shows a graph of the result of the reaction current-electric field potential measurement (C-V measurement) in the example 1.

FIG. 3 shows a graph of the result of the gas chromatography in the example

FIG. 4 shows a graph of the result of the liquid chromatography in the example 1.

DESCRIPTION OF EMBODIMENTS

One exemplary embodiment of the present disclosure is described below.

(Step (a))

In step (a), a device for reducing carbon dioxide is prepared. As shown in FIG. 1, the device includes a vessel 21, a working electrode 11, and a counter electrode 13. An electrolytic solution 15 is held in the vessel 21. An example of the electrolytic solution 15 is a potassium hydrogen carbonate aqueous solution. The electrolytic solution 15 contains carbon dioxide. It is preferable that the electrolytic solution 15 is mild acidic in the condition where carbon dioxide is dissolved in the electrolytic solution 15.

The working electrode 11 contains boron. The working electrode 11 may be fabricated as follows. First, boron particles are dispersed in an organic solvent to form slurry. Next, the slurry is applied to a porous conductive base material to obtain a working electrode. This base material preferably has a shape of a film. An example of the base material includes a carbon paper, a noble metal substrate, a glassy carbon substrate, and a conductive silicon substrate.

The working electrode may be formed by a sputtering method.

The working electrode 11 is in contact with the electrolytic solution 15. To be exact, the boron included in the working electrode 11 is in contact with the electrolytic solution 15. As shown in FIG. 1, the working electrode 11 is immersed in the electrolytic solution 15. As long as the boron is in contact with the electrolytic solution 15, only a part of the working electrode 11 may be immersed in the electrolytic solution 15.

The counter electrode contains metal. An example of the preferred metal includes platinum, gold, silver, copper, nickel, and titanium. As long as the metal is not electrolyzed, the material of the metal is not limited.

The counter electrode 13 is in contact with the electrolytic solution 15. To be exact, the metal of the counter electrode 13 is in contact with the electrolytic solution 15. As shown in FIG. 1, the counter electrode 13 is immersed in the electrolytic solution 15. As long as the metal is in contact with the electrolytic solution 15, only a part of the counter electrode 13 may be immersed in the electrolytic solution 15.

As shown in FIG. 1, it is preferable that the vessel 21 includes a tube 17. Carbon dioxide is supplied through the tube 17 to the electrolytic solution 15. One end of the tube 17 is immersed in the electrolytic solution 15.

It is preferred that a solid electrolyte membrane 16 is provided in the vessel 21. The reason for providing the solid electrolyte membrane 16 is described later in step (b). The solid electrolyte membrane 16 is interposed between the working electrode 11 and the counter electrode 13 to divide the electrolytic solution 15 into a first liquid 15L and a second liquid 15R. The counter electrode 13 is in contact with the first liquid 15L. The working electrode is in contact with the second liquid 15R.

(Step (b))

In step (b), a negative voltage and a positive voltage are applied to the working electrode 11 and the counter electrode 13, respectively. This causes the carbon dioxide contained in the electrolytic solution 15 (to be exact, the second liquid 15R) to be reduced on the working electrode 11. As a result, at lease one selected from carbon monoxide, formic acid, and methane is generated on the working electrode 11. On the counter electrode 13, water is oxidized to form oxygen.

It is preferred to use a potentiostat 14 to apply a potential difference is applied between the working electrode 11 and the counter electrode 13.

The potential difference applied between the working electrode 11 and the counter electrode 13 is preferably not less than 2.0 volts. This corresponds to the fact that carbon dioxide reducing current is measured at not more than −0.7 volts (and not less than −1.5 volts) in the example 1, which is described later.

In the preferable embodiment, the solid electrolyte membrane 16 is provided. Only a proton penetrates the solid electrolyte membrane 16. An example of the solid electrolyte membrane 16 includes a Nafion (Registered Trade Mark) film, which is available from Dupont Kabushiki Kaisha.

The solid electrolyte membrane 16 prevents a reverse reaction on the counter electrode 13. Namely, when the carbon monoxide, formic acid, or methane, which is generated on the working electrode 11, reaches the counter electrode 13, it is oxidized on the counter electrode 13 and returns to carbon dioxide. The solid electrolyte membrane 16 prevents this reverse reaction.

As shown in FIG. 1, it is preferred that a reference electrode 12 is provided. The reference electrode 12 is in contact with the electrolytic solution 15. When the solid electrolyte membrane 16 is used, the reference electrode 12 is in contact with the second liquid 15R. The reference electrode 12 is electrically connected to the working electrode 11. An example of the reference electrode 12 is a silver/silver chloride electrode.

The present device and method is described in more detail by the following example.

Example 1

Particles of boron (B particle, Mitsuwa Chemicals Co., Ltd, purity of 96%) having an average particle size of 8 microns are disposed, with a distribution density of 1×10⁷ particle/cm², on a conductive carbon paper (CP) having a thickness of 0.5 mm, thereby making an electrode catalyst (working electrode) according to the present subject matter.

Using this electrode catalyst, electrochemical reducing reaction of CO₂ was performed.

FIG. 1 shows a structural drawing of the electrochemical cell used for this measurement.

The electrochemical cell includes three electrodes, i.e., the boron particle supported electrode as set forth above as the working electrode 11, a silver/silver chloride electrode (Ag/AgCl electrode) as the reference electrode 12, and a platinum electrode (Pt-electrode) as the counter electrode 13.

The electric potential applied to the electrode was changed by using potensiostat 14, and the reducing reaction of CO₂ was performed and evaluated.

An electrolyte 15, 0.1M potassium bicarbonate aqueous solution (KHCO₃ aqueous solution) was used.

The working electrode 11 and the counter electrode 13 were partitioned off with a solid electrolyte membrane 16 to prevent the gases produced by catalytic reaction from being mixed.

CO₂ gas was introduced into the electrolyte 15 through the gas introduction tube 17 arranged in the vessel 21 by being bubbled in a KHCO₃ electrolytic solution 15.

First of all, (1) nitrogen gas was introduced into and electrolyte for 30 minutes with a flow rate of 200 ml/min, keeping a bubbling state to exclude CO₂ from the electrolyte solution. Under this condition, the electric potential was changed, and a curve of reaction electric current-electrolysis voltage (C-V curve) was measured.

Next, (2) the gas was switched from nitrogen to CO₂ and the CO₂ gas was introduced into the electrolyte 15 for 30 minutes with the same flow rate of 200 ml/min so that the electrolyte 15 was saturated with CO₂. Under this condition, the electric potential was changed, and C-V curve was measured.

A reaction electric current by CO₂ reducing reaction was evaluated by taking a difference between the C-V curve in the state (2) (the state saturated with CO₂) and the C-V curve in the state (1) (the state that CO₂ was excluded).

FIG. 2 shows the result of the difference between the two curves.

In this figure, the state that the current value (vertical axis) is negative shows that CO₂ reducing reaction has occurred.

As shown in FIG. 2, at the applied voltage is around −0.7V, a reaction electric current changes from zero to negatively in the experimental result of this example.

In other words, when the electrode catalyst including B particles is use, the reducing electric current of CO₂ was observed at the voltage of approximately −0.7V with respect to the silver/silver chloride electrode (Ag/AgCl electrode) as the reference electrode.

This result means that reducing reaction has started at about −0.5V in a case using the standard hydrogen-electrode.

On the other hand, when a CO₂ reducing experiment was conducted with an electrode catalyst of Cu in the same measurement system, the voltage smaller than −1.1 V (i.e., larger in the absolute value) was necessary to cause the reducing reaction of CO₂. This comparison shows that that electrode catalyst which includes boron is effective in reduction of voltage for reducing reaction of CO₂.

Next, the product of reducing reaction of CO₂ using the electrode on which the B particle was supported gave was analyzed.

For the analysis of the gas components, gas chromatograph of the hydrogen flame ion detector (FID) method was employed, and for the analysis of liquid components, a liquid chromatograph of the UV detection method was employed.

FIG. 3 shows the measurement result of detected methane (CH₄), ethylene (C₂H₄) and ethan (C₂H₆) with a gas chromatograph of FID.

By using a separate column of PrapakQ and controlling a valve with a predetermined time-sequence, the FID gas chromatograph is programmed so that CH₄ is detected at around 1.5 minutes after the start of the measurement, C₂H₄ is detected at around 4.5 minutes, and C₂H₆ is detected at around 6.5 minutes, respectively.

As a result, the peaks of voltage were observed by time domain which corresponds to those as shown in FIG. 3, and it was confirmed that CH₄, C₂H₄ and C₂H₆ were generated.

The measurement result of formic acid (HCOOH) by the liquid chromatograph is shown in FIG. 4.

By using a column of TSKgel SCX-H+, the liquid chromatograph was set so that a peak in HCOOH might be detected around 11.5 minutes after start of the measurement.

As a result, as shown in FIG. 4, a peak of the voltage was observed in the range corresponding to this time.

As a result, it was confirmed that HCOOH was generated by the reducing reaction of CO₂ by using the electrode catalyst that includes B particle. As set forth above, the generation of methane (CH₄), ethylene (C₂H₄), Ethan (C₂H₆) and formic acid (HCOOH) were confirmed finally by the results of analysis of the product produced by catalytic reaction.

Comparative Example 1

For a comparison, electrolytic reaction was measured with only the carbon paper (CP) which was used to support a boron particle. As a result, electric current by reducing reaction of CO₂ was not observed and it was confirmed that CP was inactive for reducing of CO₂. The product by electrolytic reaction was only hydrogen (H₂).

Comparative Example 2

For another comparison, electrolytic reaction was measured with Silicon (Si) substrate. As a result, hydrogen (H₂) was a main product as for the product by the electrolysis reaction, and hydrocarbon or formic acid (HCOOH) was not generated.

INDUSTRIAL APPLICABILITY

The present device and method provide a novel method for reducing carbon dioxide. 

1. A method for reducing carbon dioxide by using a device for reducing carbon dioxide, the method comprising: a step (a) of preparing the device, the device comprising: a vessel; a working electrode, and a counter electrode, wherein: an electrolytic solution is held in the vessel, the working electrode is composed of a conductive base material on which a boron particle is supported, the counter electrode contains metal, the boron is in contact with the electrolytic solution, the metal is in contact with the electrolytic solution, and the electrolytic solution contains the carbon dioxide; and a step (b) of applying a voltage between the working electrode and the counter electrode, thereby reducing the carbon dioxide contained in the electrolytic solution.
 2. The method according to claim 1, wherein: the vessel comprises a solid electrolyte membrane, and the solid electrolyte membrane is interposed between the working electrode and the counter electrode.
 3. The method according to claim 1, wherein in the step (b), the voltage applied between the working electrode and the counter electrode is not less than 2.0 volts.
 4. The method according to claim 1, wherein in the step (b), at least one of methane, ethylene, ethan, and formic acid is generated. 5-11. (canceled)
 12. The method according to claim 1, wherein the conductive base material is a carbon paper, a noble-metal substrate, a glassy carbon substrate, or a conductive silicon substrate. 